Print head for additive manufacturing system

ABSTRACT

A system is disclosed for additively manufacturing a composite structure. The system may include a support, and a print head operatively connected to and moveable by the support. The print head may include a supply of continuous reinforcement, an outlet configured to discharge the continuous reinforcement, and a tensioning module disposed between the supply and outlet. The tensioning module may be configured to generate a signal indicative of a tension in the continuous reinforcement. The system may also include a processor programmed to selectively cause the supply to dispense the continuous reinforcement based on the signal.

RELATED APPLICATION

This application is based on and claims the benefit of priority fromU.S. Provisional Application No. 62/706,825 that was filed on Sep. 11,2020, the contents of which are expressly incorporated herein byreference.

TECHNICAL FIELD

The present disclosure relates generally to a manufacturing system and,more particularly, to a print head for an additive manufacturing system.

BACKGROUND

Continuous fiber 3D printing (a.k.a., CF3D®) involves the use ofcontinuous fibers embedded within material discharging from a moveableprint head. A matrix is supplied to the print head and discharged (e.g.,extruded and/or pultruded) along with one or more continuous fibers alsopassing through the same head at the same time. The matrix can be atraditional thermoplastic, a liquid thermoset (e.g., an energy-curablesingle- or multi-part resin), or a combination of any of these and otherknown matrixes. Upon exiting the print head, a cure enhancer (e.g., a UVlight, a laser, an ultrasonic emitter, a heat source, a catalyst supply,etc.) is activated to initiate, enhance, and/or complete curing of thematrix. This curing occurs almost immediately, allowing for unsupportedstructures to be fabricated in free space. And when fibers, particularlycontinuous fibers, are embedded within the structure, a strength of thestructure may be multiplied beyond the matrix-dependent strength. Anexample of this technology is disclosed in U.S. Pat. No. 9,511,543 thatissued to TYLER on Dec. 6, 2016.

Although continuous fiber 3D printing provides for increased strength,compared to manufacturing processes that do not utilize continuous fiberreinforcement, care must be taken to ensure proper wetting of the fiberswith the matrix, proper cutting of the fibers, automated restartingafter cutting, proper compaction of the matrix-coated fibers afterdischarge, and proper curing of the compacted material. An exemplaryprint head that provides for at least some of these functions isdisclosed in U.S. Patent Application Publication 2019/0315057 thatpublished on Oct. 17, 2019 (“the '057 publication”).

While the print head of the '057 publication may be functionallyadequate for many applications, it may be less than optimal. Forexample, the print head may lack accuracy in placement, cutting,compaction, and/or curing that is required for other applications. Thedisclosed print head and system are directed at addressing one or moreof these issues and/or other problems of the prior art.

SUMMARY

In one aspect, the present disclosure is directed to a system foradditively manufacturing a composite structure. The system may include asupport, and a print head operatively connected to and moveable by thesupport. The print head may include a supply of continuousreinforcement, an outlet configured to discharge the continuousreinforcement, and a tensioning module disposed between the supply andoutlet. The tensioning module may be configured to generate a signalindicative of a tension in the continuous reinforcement. The system mayalso include a processor programmed to selectively cause the supply todispense the continuous reinforcement based on the signal.

In another aspect, the present disclosure is directed to a method ofadditively manufacturing a composite structure. The method may includedirecting a continuous reinforcement from a supply of a print head to anoutlet, and generating a signal indicative of a tension in thecontinuous reinforcement at a location between the supply and theoutlet. The method may also include selectively causing the supply todispense the continuous reinforcement based on the signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of an exemplary disclosed additivemanufacturing system;

FIGS. 2 and 3 are diagrammatic illustrations of an exemplary disclosedprint head that may form a portion of the additive manufacturing systemof FIG. 1;

FIG. 4 is a cross-sectional illustration of an exemplary disclosedreinforcement supply portion of the print head of FIGS. 2 and 3;

FIGS. 5-8 are diagrammatic illustrations of exemplary disclosed guideportions of the print head of FIGS. 2 and 3;

FIG. 9 is a cross-sectional illustration of an exemplary discloseddebris collecting portion of the print head of FIGS. 2 and 3;

FIGS. 10 and 11 are diagrammatic and cross-sectional illustrations,respectively, of an exemplary disclosed tensioning portion of the printhead of FIGS. 2 and 3;

FIGS. 12 and 13 are diagrammatic and cross-sectional illustrations,respectively, of an exemplary disclosed matrix supply portion of theprint head of FIGS. 2 and 3;

FIGS. 14 and 15 are diagrammatic illustrations and FIG. 16 is across-sectional illustration of an exemplary disclosed clamping portionof the print head of FIGS. 2 and 3;

FIGS. 17 and 18 are diagrammatic and cross-sectional illustrations,respectively, of an exemplary disclosed wetting portion of the printhead of FIGS. 2 and 3;

FIGS. 19 and 20 are diagrammatic illustrations of exemplary disclosedfeeding, cutting, compacting and curing portions of the print head ofFIGS. 2 and 3;

FIG. 21 is a diagrammatic illustration of the exemplary disclosedcutting, compacting and curing portions of FIGS. 19 and 20;

FIGS. 22 and 23 are cross-sectional and exploded view illustrations ofthe exemplary disclosed cutting portion of FIGS. 19-21;

FIGS. 24 and 25 are diagrammatic illustrations and FIG. 26 is across-sectional illustration of the curing and compacting portions ofFIGS. 19-21;

FIGS. 27, 28, 29, 30, 31, 32 and 33 are exploded view and diagrammaticillustrations of exemplary components of the curing and compactingportion of FIGS. 24 and 25; and

FIGS. 34, 35, 36, 37 and 38 are diagrammatic illustrations showingoperation of the feeding, cutting, compacting and curing portions ofFIGS. 19 and 20.

DETAILED DESCRIPTION

The term “about” as used herein serves to reasonably encompass ordescribe minor variations in numerical values measured by instrumentalanalysis or as a result of sample handling. Such minor variations may bein the order of plus or minus 0% to 10%, plus or minus 0% to 5%, or plusor minus 0% to 1%, of the numerical values.

The term “substantially” as used herein refers to a majority of, ormostly, as in at least about 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%,98%, 99%, 99.5%, 99.9%, 99.99%, or at least about 99.999% or more.

FIG. 1 illustrates an exemplary system 10, which may be used tomanufacture a composite structure 12 having any desired shape, size,configuration, and/or material composition. System 10 may include atleast a support 14 and a head 16. Head 16 may be coupled to and moveableby support 14 during discharge of a composite material (shown as C). Inthe disclosed embodiment of FIG. 1, support 14 is a robotic arm capableof moving head 16 in multiple directions during fabrication of structure12. Support 14 may alternatively embody a gantry (e.g., anoverhead-bridge gantry, a single-post gantry, etc.) or a hybridgantry/arm also capable of moving head 16 in multiple directions duringfabrication of structure 12. Although support 14 is shown as beingcapable of 6-axis movements, it is contemplated that any other type ofsupport 14 capable of moving head 16 in the same or a different mannercould also be utilized. In some embodiments, a drive or coupler 18 maymechanically join head 16 to support 14, and include components thatcooperate to move portions of and/or supply power and/or materials tohead 16.

Head 16 may be configured to receive or otherwise contain a matrix that,together with a continuous reinforcement, makes up the compositematerial discharging from head 16. The matrix may include any type ofmaterial that is curable (e.g., a liquid resin, such as a zero-volatileorganic compound resin, a powdered metal, etc.). Exemplary resinsinclude thermosets, single- or multi-part epoxy resins, polyesterresins, cationic epoxies, acrylated epoxies, urethanes, esters,thermoplastics, photopolymers, polyepoxides, thiols, alkenes,thiol-enes, and more. In one embodiment, the matrix inside head 16 maybe pressurized, for example by an external device (e.g., by an extruderor another type of pump—not shown) that is fluidly connected to head 16via a corresponding conduit (not shown). In another embodiment, however,the pressure may be generated completely inside of head 16 by a similartype of device. In yet other embodiments, the matrix may be gravity-fedinto and/or through head 16. For example, the matrix may be fed intohead 16 and pushed or pulled out of head 16 along with one or morecontinuous reinforcements. In some instances, the matrix inside head 16may benefit from being kept cool and/or dark (e.g., to inhibit prematurecuring or otherwise obtain a desired rate of curing after discharge). Inother instances, the matrix may need to be kept warm for similarreasons. In either situation, head 16 may be specially configured (e.g.,insulated, temperature-controlled, shielded, etc.) to provide for theseneeds.

The matrix may be used to coat any number of continuous reinforcements(e.g., separate fibers, tows, rovings, ribbons, socks, sheets and/ortapes of continuous material) and, together with the reinforcements,make up a portion (e.g., a wall) of composite structure 12. Thereinforcements may be stored within (e.g., on one or more separateinternal creels 19) or otherwise passed through head 16 (e.g., fed fromone or more external spools—not shown). When multiple reinforcements aresimultaneously used (e.g., interwoven, one on top of another, adjacenttracks, etc. that are combined prior to and/or after entering head 16),the reinforcements may be of the same material composition and have thesame sizing and cross-sectional shape (e.g., circular, square,rectangular, etc.), or a different material composition with differentsizing and/or cross-sectional shapes. The reinforcements may include,for example, carbon fibers, vegetable fibers, wood fibers, mineralfibers, glass fibers, metallic wires, optical tubes, etc. It should benoted that the term “reinforcement” is meant to encompass bothstructural and non-structural types of continuous materials that are atleast partially encased in the matrix discharging from head 16.

The reinforcements may be exposed to (e.g., at least partially coatedwith) the matrix while the reinforcements are inside head 16, while thereinforcements are being passed to head 16, and/or while thereinforcements are discharging from head 16. The matrix, dryreinforcements, and/or reinforcements that are already exposed to thematrix (e.g., pre-impregnated reinforcements) may be transported intohead 16 in any manner apparent to one skilled in the art. In someembodiments, a filler material (e.g., chopped fibers) may be mixed withthe matrix before and/or after the matrix coats the continuousreinforcements.

As will be explained in more detail below, one or more cure enhancers(e.g., a UV light, an ultrasonic emitter, a laser, a heater, a catalystdispenser, etc.) may be mounted proximate (e.g., within, on, oradjacent) head 16 and configured to enhance a cure rate and/or qualityof the matrix as it discharges from head 16. The cure enhancer(s) may becontrolled to selectively expose portions of structure 12 to energy(e.g., to UV light, electromagnetic radiation, vibrations, heat, achemical catalyst, etc.) during material discharge and the formation ofstructure 12. The energy may trigger a chemical reaction to occur withinthe matrix, increase a rate of the chemical reaction, sinter the matrix,harden the matrix, or otherwise cause the matrix to cure as itdischarges from head 16. The amount of energy produced by the cureenhancer(s) may be sufficient to cure the matrix before structure 12axially grows more than a predetermined length away from head 16. In oneembodiment, structure 12 is cured before the axial growth length becomesequal to an external diameter of the matrix-coated reinforcement.

The matrix and/or reinforcement may be discharged from head 16 via oneor more different modes of operation. In a first exemplary mode ofoperation, the matrix and/or reinforcement are extruded (e.g., pushedunder pressure and/or mechanical force) from head 16 as head 16 is movedby support 14 to create the 3-dimensional trajectory within alongitudinal axis of the discharging material. In a second exemplarymode of operation, at least the reinforcement is pulled from head 16,such that a tensile stress is created in the reinforcement duringdischarge. In this mode of operation, the matrix may cling to thereinforcement and thereby also be pulled from head 16 along with thereinforcement, and/or the matrix may be discharged from head 16 underpressure along with the pulled reinforcement. In the second mode ofoperation, where the matrix is being pulled from head 16 with thereinforcement, the resulting tension in the reinforcement may increase astrength of structure 12 (e.g., by aligning the reinforcements,inhibiting buckling, etc.), while also allowing for a greater length ofunsupported structure 12 to have a straighter trajectory. That is, thetension in the reinforcement remaining after curing of the matrix mayact against the force of gravity (e.g., directly and/or indirectly bycreating moments that oppose gravity) to provide support for structure12.

The reinforcement may be pulled from head 16 as a result of head 16being moved by support 14 away from an anchor (e.g., a print bed, atable, a floor, a wall, a surface of structure 12, etc.—not shown). Inparticular, at the start of structure formation, a length ofmatrix-impregnated reinforcement may be pulled and/or pushed from head16, deposited onto the anchor, and at least partially cured, such thatthe discharged material adheres (or is otherwise coupled) to the anchor.Thereafter, head 16 may be moved away from the anchor (e.g., viacontrolled regulation of support 14), and the relative movement maycause the reinforcement to be pulled from head 16. It should be notedthat the movement of reinforcement through head 16 could be assisted(e.g., via one or more internal feed mechanisms), if desired. However,the discharge rate of reinforcement from head 16 may primarily be theresult of relative movement between head 16 and the anchor, such thattension is created within the reinforcement. It is contemplated that theanchor could be moved away from head 16 instead of or in addition tohead 16 being moved away from the anchor.

A controller 20 may be provided and communicatively coupled with support14, head 16, and any number of the cure enhancer(s). Each controller 20may embody a single processor or multiple processors that are speciallyprogrammed or otherwise configured to control an operation of system 10.Controller 20 may further include or be associated with a memory forstoring data such as, for example, design limits, performancecharacteristics, operational instructions, tool paths, and correspondingparameters of each component of system 10. Various other known circuitsmay be associated with controller 20, including power supply circuitry,signal-conditioning circuitry, solenoid driver circuitry, communicationcircuitry, and other appropriate circuitry. Moreover, controller 20 maybe capable of communicating with other components of system 10 via wiredand/or wireless transmission.

One or more maps may be stored in the memory of controller 20 and usedby controller 20 during fabrication of structure 12. Each of these mapsmay include a collection of data in the form of lookup tables, graphs,and/or equations. In the disclosed embodiment, controller 20 may bespecially programmed to reference the maps and determine movements ofhead 16 required to produce the desired size, shape, and/or contour ofstructure 12, and to responsively coordinate operation of support 14,the cure enhancer(s), and other components of head 16.

An exemplary head 16 is disclosed in greater detail in FIGS. 2 and 3. Ascan be seen in these figures, head 16 may include a housing 22 that isconfigured to hold, enclose, contain, and/or provide mounting for theremaining components of head 16. Housing 22 may include any number ofpanels connected to each other to form a multi-sided enclosure thatsupports and protects the other components. In the disclosed embodiment,the enclosure of housing 22 is generally T-shaped, having an uppergenerally horizontal plate 24 (e.g., as viewed from the perspective ofFIG. 2) and one or more lower plates 26 (e.g., a primary plate 26 a andan orthogonally oriented gusset 26 b) that are generally vertical andintersect with upper plate 24. The other components of head 16 may bemounted to a front and/or back of lower plate(s) 26, and to an underside of upper plate 24. As will be explained in more detail below, somecomponents may extend downward past a terminal end of lower plate(s) 26.Likewise, some components may extend transversely from lower plate(s) 26past outer edges of upper plate 24.

Upper plate 24 may be generally square, while lower plate 26 may beelongated. Lower plate 26 may have a wider proximal end rigidlyconnected to a general center of upper plate 24 and a narrower distalend that is cantilevered from the proximal end. Coupler 18 may beconnected to upper plate 24 at a side opposite lower plate(s) 26 andused to quickly and releasably connect head 16 to support 14. One ormore racking mechanisms (e.g., handles, hooks, eyes, etc.—not shown) maybe located adjacent coupler 18 and used to rack head 16 (e.g., duringtool changing) when head 16 is not connected to support 14.

As shown in FIGS. 2 and 3, any number of components of head 16 may bemounted to housing 22 via upper and/or lower plates 24, 26. For example,a reinforcement supply module 44 and a matrix supply module 46 may beoperatively connected to upper plate 24, while a tensioning module 48, aclamping module 50, a wetting module 52, an outlet 54, a cutting module56, and a compacting/curing module 58 may be operatively mounted tolower plate(s) 26. It should be noted that other mounting arrangementsmay also be possible. Any number of conduits, valves, actuators,chillers, heaters, manifolds, wiring harnesses, and other similarcomponents may be co-mounted to one or more of upper and/or lower plates24, 26, if desired.

As will be described in more detail below, the reinforcement may pay outfrom module 44, pass through and be tension-regulated by module 48, bewetted with matrix in module 52 (e.g., as supplied by module 46) and bedischarged through outlet 54. After discharge, the matrix-wettedreinforcement may be selectively severed via module 56 (e.g., whilebeing held stationary by module 50) and thereafter compacted and/orcured by module 58.

As shown in FIG. 4, module 44 may be a subassembly that includescomponents configured to selectively allow and/or drive rotation ofcreel 19, while simultaneously translating creel 19 in an axialdirection during the rotation. As will be discussed in more detailbelow, the rotation of creel 19 may be regulated by controller 20(referring to FIG. 1) based, at least in part, on a detected positionand/or status of module 48. This responsive rotational regulation mayhelp to maintain one or more desired levels of tension within thereinforcement (e.g., a nominal tension during normal discharge; a lowerlevel during free-space printing; a higher level during severing, etc.).The axial translation of creel 19 may help the reinforcement to feedsubstantially perpendicularly from creel 19 (e.g., relative to an axis59 of creel 19), regardless of an axial location at which thereinforcement is being fed from creel 19. That is, the reinforcement mayinitially be loaded onto creel 19 in a spiraling motion and, unlessotherwise accounted for, the feed location of the reinforcement fromcreel 19 may shift axially from one end of creel 19 to an opposing endduring unspooling. This axial shifting of the feed point could causedegradation to the reinforcement and/or interrupt smooth operation ofdownstream components (e.g., of module 48 that is located immediatelydownstream). Accordingly, by translating creel 19 along axis 59 (e.g.,at a rate corresponding to the spiral of the reinforcement on creel 19)during unspooling, the reinforcement may be maintained at a relativelyconstant feed location and angle α relative to the rest of head 16. Thismay reduce degradation of the reinforcement and help ensure smoothfeeding into and operation of module 48. In some embodiments, theconstant feed location and/or angle α may additionally or alternativelyinhibit untwisting of the reinforcement during unspooling.

The subassembly components of module 44 may include, among other things,a translating actuator 60 rigidly connected to at least one of upper andlower plates 24, 26 (e.g., to only upper plate 24), and a rotatingactuator 62 operatively connecting creel 19 to translating actuator 60.During operation, controller 20 may selectively activate translatingactuator 60 and cause rotating actuator 62 and creel 19 to reciprocatetogether in a direction generally orthogonal to primary plate 26 a(referring to FIGS. 2 and 3). Controller 20 may coordinate thisreciprocation in coordination with rotation of actuator 62 andunspooling of creel 19. It should be noted that the unspooling of creel19 may be based primarily on the tension requirements of module 48, andthat the reciprocation is controlled in response to the unspooling.

In one example, translating actuator 60 may include a rail 64, acarriage 66 configured to slide along rail 64, and a motor 68 configuredto cause the sliding of carriage 66. Motor 68 may embody an electric,hydraulic, pneumatic, or other type of motor connected to carriage 66(e.g., by way of a lead screw 70). It is contemplated that another typeof translating actuator (e.g., a cylinder) could be used, if desired.

In one example, rotating actuator 62 may be rigidly connected tocarriage 66 of translating actuator 60 via an arm 72. A rotary actuator74 may be fixedly connected to arm 72, and include a rotor 76rotationally affixed to creel 19 (e.g., to a spool core 78). In oneexample, spool core 78 may be easily removed (e.g., slipped off axially)from rotor 76 and rotationally locked to rotor 76 (e.g., via a keyway, afriction device, etc.). Rotor 76 may be rotationally supported by arm 72via one or more bearings 79.

The coordination by controller 20 of the rotation and translation ofcreel 19 may be performed multiple different ways. In one example, aninitial spiral rate of the reinforcement on the spool may be assumed orprovided by the reinforcement manufacturer, and controller 20 maygenerate a feedforward command based on the assumption to translate androtate creel at corresponding rates. In some embodiments, a decreasingdiameter of creel 19 (e.g., due to consumption of the reinforcement) mayaffect the assumed or provided rate of spiral. Accordingly, the diametermay also be assumed (e.g., based on known and/or commanded motions,consumption, and/or payout from head 16), measured (e.g., via a diametersensor—not shown), and/or back calculated based on reinforcement payoutand/or head velocity and accounted for by controller 20.

In another example, the angle α of the reinforcement paying out from thespool of creel 19 may be directly measured. In this example, controller20 may generate a feedback signal that adjusts the rotation and/ortranslation rate and/or position, such that the angle of thereinforcement is maintained within a threshold (e.g., α≈15°) of 90°relative to the axis of creel 19. Any number of angle and/or position(e.g., optical, mechanical, etc.) sensors 81 may be employed for thispurpose and connected to controller 20. It is contemplated that both thefeedforward and feedback signals may be utilized by controller 20 toregulate the rotation and/or translation of creel 19, if desired. It isalso contemplated that the rotation may be regulated solely based on thetension with the reinforcement and only the translation may be adjustedbased on the payout angle of the reinforcement.

In some applications, it may not be possible or feasible to completelyeliminate angle α during unspooling of creel 19. In these applications,one or more centering guides 80 may be placed between modules 46 and 48(e.g., alone or in series) that further reduce angle α. Exemplary guides80 are illustrated in FIGS. 5-8.

The example guide 80 of FIG. 5 may include any number of rotaryredirects 82 arranged into any number of pairs that are substantiallyorthogonal to each other. For example, a first pair (one shown inphantom) of redirects 82 may be oriented parallel to each other andgenerally orthogonal to axis 59, and a second pair (one shown inphantom) of redirects 82 may be oriented parallel to each other andparallel to axis 59. Two sets of orthogonal redirects 82 may function tocapture the reinforcement therebetween, eliminating a risk of losingcontrol over reinforcement placement. However, it is contemplated that,alternatively, one pair of parallel redirects 82 (e.g., the pair that isorthogonal to axis 59) and a single additional redirect 82 (e.g., aredirect that is parallel to axis 59) could be utilized, wherein thesingle additional redirect 82 is located at an extreme or maximumposition within an expected range of reinforcement motion (i.e., suchthat the reinforcement always wraps at least partially around the singleadditional redirect 82, regardless of feed location from the spool ofcreel 19). It is also contemplated that only two orthogonal redirects 82(i.e., no parallel pairs) could alternatively be utilized (i.e., suchthat the reinforcement always wraps at least partially around each ofthe redirects), if desired.

In one embodiment, the redirect(s) 82 parallel to axis 59 may beout-of-plane from the redirect(s) 82 that are perpendicular to axis 59.This may allow the reinforcement to twist (e.g., by about 90°) betweenthe redirects 82. That is, the reinforcement may have a generallyrectangular cross-section, with a width greater than a height. With theout-of-plane configuration, the redirect(s) 82 may always engage thewidth of the reinforcement, thereby exerting a lower pressure on thereinforcement and reducing a likelihood of the reinforcement crumplingor folding. When passing from module 46 to module 48, this may requirethe reinforcement to twist +90° to properly engage the upstreamredirect(s) 82, and twist back −90° to properly engage the downstreamredirect(s) 82. A spacing between planes of the upstream and downstreamredirects may be large enough to accommodate a single 90° twisttherebetween. In one embodiment, the axial distance between the upstreamand downstream redirects may be at least equal to two times the width ofthe reinforcement. Once the reinforcement is threaded between theupstream and downstream redirects 82, a tension placed on thereinforcement by module 48 may help maintain the desired engagement ofthe reinforcements with the upstream and downstream redirects 82.

Because redirects 82 may act on the reinforcement while thereinforcement is dry (e.g., before being wetted with matrix by module52), a diameter of each redirect may be small because the individualfilaments of the reinforcement may move more easily relative to eachother as the reinforcement bends around the redirects 82. Each redirectmay be fabricated from a smooth and/or low-surface energy material. Thismaterial may include, for example, a polished steel or a plastic (e.g.,UHMW, PTFE, FEP, an acetal homopolymer such as Polyoxymethylene, afluoropolymer, a coated metal, etc.).

In an alternative configuration shown in FIG. 6, guide 80 may beconfigured to translate with or in place of translation of creel 19. Forexample, guide 80 may include a redirect 82 connected to a linearactuator 84 (e.g., a carriage/lead screw/motor configuration). In thisconfiguration, guide 80 may move axially with the unspoolingreinforcement, such that the angle α is reduced or reduced further thantranslation of creel 19 alone. It is contemplated that, when both guide80 and creel 19 translate, the translation of creel 19 may be greaterthan the translation of guide 80.

In one example, in addition or as an alternative to translating,redirect 82 may tilt or pivot relative to linear actuator 84. Forexample, redirect 82 may be elongated, having an eyelet (shown in FIG.6) or other guide feature (e.g., roller—see FIG. 7) 86 for receiving thereinforcement at a distal end and being pivotally connected to linearactuator 84 at an opposing end. Redirect 82 may be biased (e.g., via atorsional spring 89) to a center or perpendicular position (e.g., wherea is minimized). During operation, as the reinforcement unspools fromcreel 19 and nears the extreme ends of the associated spool, anincreasing tension in the reinforcement may cause pivoting of redirect82 toward the respective end. This may limit the amount of tensionallowed to pass through the reinforcement, thereby reducing damage tothe reinforcement.

In an alternative embodiment, redirect 82 may be a translating deviceinstead of a rotating or pivoting device. For example, as shown in FIG.8, redirect 86 may be a shuttle configured to oscillate within acorresponding slot in the direction of axis 59. In the disclosed exampleof FIG. 8, redirect 86 may still be associated with linear actuator 84(e.g., the slot may be formed within a carriage of linear actuator 84).However, it is contemplated that the oscillating redirect 86 couldalternatively be associated with a stationary slot, if desired.

In some applications, even with the care taken to reduce damage to thereinforcement during travel between modules 44 and 48 (e.g., duringtravel through guide 80), some damage may still occur. For example,individual fibers making up the reinforcement may break, fray, and/orfuzz. If not otherwise accounted for, the broken off fibers, frayedfibers, fiber fuzz and/or other associated debris could inhibit (e.g.,build up and restrict, obstruct, clog, etc.) operations of head 16. Thissituation may be exacerbated when the debris has been wetted with matrixand begins to agglomerate. Accordingly, in these applications, a debrisremoval unit (“unit”) 88 may be placed at any location downstream ofguide 80 and upstream of module 52 to collect the debris before itbecomes problematic. It should be noted that a greater amount of debrismay be collected by unit 88 as unit 88 is moved downstream of a greaternumber of debris-generating components. In one example, unit 88 may beplaced immediately upstream of module 52.

As shown in FIG. 9, unit 88 may include, among other things, a chamber90 through which the reinforcement R passes during its travel towardmodule 52. An inlet and an outlet of chamber 90 may be reduced, suchthat a pressure of the associated enclosed space may be controlled. Avacuum port 92 may be located at one side of chamber 90 (e.g., at agravitationally lower side), and a filter 94 may be placed between thereinforcement and vacuum port 92. Vacuum port 92 may generate a flow ofair (or another inert medium) across the reinforcement and throughfilter 94, wherein any debris d entrained in the flow becomes trapped.

In some embodiments, one or more agitators 96 may be located withinchamber 90 and in proximity to the reinforcement. Agitator(s) 96 mayembody any device that is configured to agitate (e.g., shake, vibrate,jiggle, wobble, etc.) the reinforcement and thereby dislodge loosedebris clinging to the reinforcement. In one example, agitator(s) 96include jets configured to direct puffs of low-pressure air againstand/or across the reinforcement. A pressure of the puffs may be greatenough to agitate the reinforcement without significantly moving thereinforcement from a direct travel path through chamber 90. In onespecific example, the pressure of the puffs may be about 1 bar abovechamber pressure.

It should be noted that unit 88 may be used to additionally oralternatively improve impregnation of the fibers. That is, agitator(s)96 may be used to loosen the fibers, allowing more space for the matrixto move in therebetween. In this embodiment, agitator(s) 96 may be usedwith or without vacuum port 92 and/or filter 94, if desired.

As shown in FIGS. 10 and 11, module 48 may be a subassembly locatedbetween modules 44 and 50 (e.g., relative to the travel of reinforcementthrough head 16) and that includes components configured to affect anamount and/or rate of the reinforcement being paid out by module 44.These components may include, among other things, a swing arm 98pivotally connected at one end (e.g., an end closest to module 44) tolower plate 26 via a pivot shaft 100, a redirect 102 rotatably mountedat each end of swing arm 98, and a rotary sensor 104 (e.g., an sensor,potentiometer, etc.—shown only in FIG. 11) connected to rotate withpivot shaft 100 (e.g., at a side of lower plate 26 opposite swing arm98).

In the disclosed embodiment, because the pivot point of swing arm 98 islocated at an end, swing arm 98 may not be balanced about the point. Ifunaccounted for, this imbalance could cause swing arm 98 to functiondifferently as head 16 is tilted to different angles. Accordingly, insome applications, a counterweight 108 may be connected to swing arm 98at a side opposite the free end of swing arm 98.

In some embodiments, swing arm 98 may be biased (e.g., via one or moresprings 106) toward a centered or neutral position. Spring 106 mayextend from one or more anchors on lower plate 26 to an end ofcounterweight 108 (e.g., a gravitationally lower end away from plate24). In this embodiment, spring 106 is a tension spring. It iscontemplated, however, that a single torsion spring mounted around pivotshaft 100 could alternatively be utilized to bias swing arm 98, ifdesired.

During operation, as the reinforcement is pulled out at an increasingrate from head 16, swing arm 98 may be caused to rotate counterclockwise(e.g., relative to the perspective of FIG. 10) to provide a generallyconstant tension (e.g., about 0-5 lbs or about 0-1 lb) within thereinforcement. This rotation may result in a similar input rotation tosensor 104, which may responsively generate an output signal directed tocontroller 20 indicative of the increasing rate. The signal may bedirected to module 44, resulting in increased payout of thereinforcement from creel 19, thereby allowing swing arm 98 to returnback towards its nominal position. As the rate of reinforcement beingpulled from head 16 decreases, spring 106 may rotate swing arm 98 in theclockwise direction to provide the generally constant tension within thereinforcement. During this clockwise motion, sensor 104 may againgenerate a signal indicative of the rotation and direct this signal tocontroller 20 for further processing and control over module 44.

One or more end-stops 109 may be associated with module 48 to limit arange of rotation of swing arm 98. In the disclosed embodiment, twodifferent end-stops are provided, including a hard end-stop 109 a and ahigh-tension end stop 109 b. Swing arm 98 may naturally rest againsthard end stop 109 a due to the bias of spring 106. Swing arm 98 beselectively driven into high-tension end stop 109 b during selectfabrication events (e.g., during a severing event).

It should be noted that, although a single module 48 is illustratedwithin print head 16, it is contemplated that multiple modules 48 couldalternatively be utilized. In this embodiment, modules 48 could be thesame or different (e.g., have different spring and/or response rates)and placed in series, if desired.

Module 46 may be configured to direct a desired amount of matrix at aspecified rate under specified conditions to module 50 for wetting ofthe reinforcements received from module 48. As shown in FIGS. 12 and 13,module 46 may be an assembly of components that receive, condition andmeter out matrix M from a disposable cartridge 110. These components mayinclude, among other things, a vessel 112 having an inlet 114 configuredto receive cartridge 110, a cap 116 configured to close off inlet 114,and an outlet 118 through which the matrix is selectively pressed fromcartridge 110. In one embodiment, vessel 112 is generally cylindrical,and cap 116 is threaded to internally receive and connect to an end ofvessel 112. A port 120 may be formed within cap 116 to allowcommunication with a pressure-regulated medium (e.g., air).

Cartridge 110 may include a generally cylindrical and flexible membrane122 having a first end and a second end. A piston 124 may be connectedat the first end to membrane 122, and an outlet port 126 may beconnected at the second end to membrane 122. With this configuration, asthe pressure-regulated medium is directed into vessel 112 (e.g., via cap116), the pressure of the medium may act against piston 124, generatinga force directed toward outlet port 126 that causes membrane 122 tocontrollably collapse. The collapse of membrane 122 may force matrix outof membrane 122 through port 126. With this configuration, a pressureand/or a flow rate of the medium into vessel 112 via inlet port 120 maycorrespond with an amount and/or a flow rate of matrix out of membrane122 through outlet port 126 and outlet 118. It is contemplated that alinear actuator rather than the pressurized medium may be used to pushagainst piston 124 and collapse flexible membrane 122, if desired. It isalso contemplated that membrane 122 may not collapse—instead, piston 124may be pushed lengthwise through membrane 122 to thereby force thematrix out of cartridge 110.

In some applications, control over the amount and/or flow rate of matrixfrom module 46 via regulation of the medium through inlet port 120 maynot be as precise as desired. In these applications, a metering valve128 may be situated downstream of vessel 112 and configured toselectively adjust the amount and/or flow rate of the matrix passing tomodule 50. In one embodiment, the matrix exiting vessel 112 may passthrough a flexible passage 130, and valve 128 may be configured toselectively pinch and thereby restrict flow through passage 130 (e.g.,in response to signals from controller 20).

During discharge of the matrix from vessel 112, care should be taken toavoid depletion of matrix from cartridge 110. For this reason, a levelsensor 132 may be associated with membrane 122 and configured togenerate a signal indicative of an amount of matrix consumed from and/orremaining within membrane 122. In the depicted example, level sensor 132is an optical sensor (e.g., a laser sensor) configured to generate abeam 134 directed through a transparent portion of vessel 112 from thedischarge end of membrane 122 to piston 124. The beam may reflect offpiston 124 and be received back at sensor 132, wherein a comparison ofoutgoing and incoming portions of the beam produces a signal indicativeof the consumed and/or remaining matrix amount. It is contemplated thatsensor 132 could alternatively be located at an opposing end ofcartridge 110 and configured to detect a location of piston 124 withoutfirst passing through membrane 122, if desired. It is furthercontemplated that a non-optical type of sensor (e.g., an embeddedmagnet/hall effect sensor) could alternatively or additionally beutilized to generate the matrix-related signal, if desired.

It should be noted that the matrix contained within membrane 122 may belight-sensitive. Accordingly, care should be taken to avoid exposurethat could cause premature curing. In the disclosed embodiment, membrane122 may be tinted, coated (internally and/or externally), or otherwiseshielded to inhibit light infiltration. For example, membrane 122 may befabricated from an amber material that inhibits (e.g., blocks) lighthaving a wavelength of about 550 nm or less. In this example, beam 134may have a wavelength greater than 550 nm, such that the amber materialdoes not disrupt its passage to and from piston 124 from the dischargeend.

In some applications, handling and/or curing characteristics of thematrix may be affected by a temperature of the matrix inside of module46. For this reason, module 46 may be selectively heated, cooled, and/orinsulated accordingly to one or more predetermined requirements of aparticular matrix packaged within cartridge 110 and loaded into vessel112. For example, one or more heating elements (e.g., electrodes) 136may be mounted inside of and/or outside of vessel 112 and configured togenerate heat conducted through membrane 122 to the matrix therein.Controller 20 may be in communication with heating element(s) 136 andconfigured to adjust the output of heating element(s) 136 based on aknown and/or detected temperatures of the matrix in module 46.

It may be important, in some situations, to insulate module 46 fromother components of head 16. In the disclosed embodiment, vessel 112 maybe mounted to housing 22 (e.g., upper and/or lower plates 24, 26) viaone or more mounting brackets 138. Mounting bracket(s) 138 may beseparated from vessel 112 by way of a first insulating layer 140 andfrom housing 22 via a second insulating layer 142. In addition, mountingbracket(s) 138 may be fabricated from a heat conducting material suchthat, if heat is transferred away from vessel 112 into mountingbracket(s) 138, the heat may be quickly dissipated to the air.

As shown in FIGS. 14, 15 and 16, clamping module 50 may be a subassemblyhaving components that cooperate to selectively clamp the reinforcementand thereby inhibit movement (e.g., any movement or only reversemovement) of the reinforcement through head 16. This may be helpful, forexample, during severing of the reinforcement away from structure 12,such that tensioning module 48 does not unintentionally pull thereinforcement back through head 16. This may also be helpful duringoff-structure movements of head 16 (e.g., when no reinforcement shouldbe paying out) and/or briefly at a start of a new payout (e.g., whiletacking the reinforcement at the anchor). In each of these scenarios,clamping module 50 may selectively function as a check-valve, ensuringunidirectional movement of the reinforcement through head 16. Byallowing at least some movement of the reinforcement at all times,damage to the reinforcement may be reduced. It is contemplated, however,that motion of the reinforcement could alternatively or selectively beinhibited in both directions when module 48 is activated, if desired.

The components of module 50 may include, among other things, a yoke 144that is removably connectable to lower plate 26, a clutched roller 146that is pivotally connected to yoke 144 via a shaft 148, and an actuator(e.g., a linear cylinder) 150 that is mounted to yoke 144 at a sideopposite roller 146 and configured to selectively engage (e.g., pressthe reinforcement against) clutched roller 146. In one embodiment, anadditional roller (clutched or free-rolling) 152 may be pivotallyconnected at an end of actuator 150 (e.g., via a shaft 154) andconfigured to engage roller 146 of yoke 144. It is contemplated that oneor both of rollers 146, 152 could be replaced with a plate or foot, ifdesired.

As shown in FIGS. 14 and 15, yoke 144 may have a generally C-shapedcross-section. The reinforcement received from module 48 may passthrough the opening of the C-shape at a location between rollers 146 and152. When actuator 150 is moved to a retracted position (e.g., during athreading event—shown in FIGS. 14-16), roller 152 may be pulled awayfrom the reinforcement, such that movement of the reinforcement throughyoke 144 in any direction is uninhibited by rollers 146 and 152. Whenactuator 150 is in an extended position (not shown), roller 152 mayforce the reinforcement downward against roller 146, thereby allowingtranslation of the reinforcement only on the payout direction whenrollers 146 and 152 rotate about their respective shafts (e.g., only inthe payout direction facilitated by internal clutches). Because rollers146 and 152 may rotate at a same rate that the reinforcement passesthrough module 50, damage to the reinforcement may be minimal (i.e.,because there is no relative motion between the reinforcement and therollers).

It may be important, in some applications, to ensure parallel alignmentbetween axis of shafts 148 and 154. Parallel alignment may promoteline-to-line contact and damage-free sandwiching of the reinforcementtherebetween. In these applications, the orientation of shaft 148 may befixed relative to yoke 144, while shaft 154 may be connected to actuator150 (e.g., to a plunger of actuator 150) via a pivot pin 156. Pivot pin156 may allow the axis of shaft 154 (and roller 152) to pivot within aplane passing through the axis of shaft 148 during engagement of roller152 with roller 146 until the line-to-line contact is achieved (e.g.,within a threshold amount). In addition, in some embodiments, one orboth of rollers 146 and 152 may be wrapped in a compliant material(e.g., rubber) to further promote parallel alignment, if desired.

During clutched operation of rollers 146 and 152, any generated torquemay be transferred back through yoke 144 to lower plate 26. For example,shafts 148 and 154 may include features (e.g., flat-sided heads) thatmechanically lock with corresponding features (e.g., slots) of yoke 144.Any rotations induced within rollers 146 and 152 that are caused byreverse motion of the reinforcement back into head 16 may be inhibitedby the mechanical lock.

The clutching of rollers 146 and 152 may allow reinforcement to bepulled through module 50, even when module 50 has been activated. Thismay allow for relaxed timing precision between cutting and feedingevents. It is contemplated that, in some applications, module 50 may beactive any time head 16 is active. This may allow for reduced part count(e.g., elimination of actuator 150) and/or increased componentreliability.

In some applications, activation of module 50 may be used to detect anoperational status of another module of head 16. For example, when theother modules of head 16 are fully operational and module 50 isactivated to clamp the continuous reinforcement, no subsequent payout ofthe continuous reinforcement should be detected. This includes motion ofhead 16 away from a point of reinforcement severance. That is, ifsevering has been commanded of module 56 by controller 20 and module 50has been previously activated, failure of module 56 to fully sever thereinforcement may correspond with additional reinforcement being pulledthrough the clutched rollers of module 50 during movement of head 16away from the severance location. The pulling of additionalreinforcement may be detected by sensor 104, and controller 20 mayrespond accordingly. For example, controller 20 may place head 16 into ahold status, thereby allowing an operator to service or replace module56.

As shown in FIGS. 17 and 18, wetting module 52 may be a subassembly thatincludes, among other things, a tubular body 158 having a fiber inlet160 configured to receive reinforcement from module 50, a matrix inlet162 (shown only in FIG. 17) configured to receive matrix from module 46,and a composite outlet 164 configured to discharge matrix-wettedreinforcements toward module 58; a first nozzle 166 removably connectedto fiber inlet 160; a second nozzle 168 removably connected to compositeoutlet 164; and a heater 170 associated with body 158 and disposedbetween fiber inlet 160 and composite outlet 164 (e.g., closer to fiberinlet 160).

Reinforcement entering module 52 may pass first through nozzle 166. Inone embodiment, nozzle 166 has a cross-sectional (e.g., rectangular,circular, triangular, or other polygonal or elliptical) shapesubstantially matching a cross-sectional shape of the reinforcement. Anarea of the cross-section may taper from a larger upstream end to asmaller downstream end. This tapering may facilitate threading of thereinforcement through nozzle 166. The area of the downstreamcross-section may be selected to be just larger than a cross-sectionalarea of the reinforcement, such that reverse passage of matrix throughthe downstream cross-section may be restricted. In one embodiment, thedownstream cross-sectional area of nozzle 166 may be 0-30% (e.g.,10-20%) greater than the cross-sectional area of the reinforcement. Aseal 172 may be disposed annularly between an outer surface of nozzle166 and an inner surface of body 158, and a fastener (e.g., a nut) 174may be used to press nozzle 166 into body 158. Body 158 may include oneor more clocking features (e.g., flat lands) that engage one or morecorresponding clocking features (e.g., flat lands) of nozzle 166, suchthat body 158 and nozzle 166 (and the reinforcement passing throughnozzle 166) may be oriented in a desired manner relative to each other(e.g., with a widest direction of the nozzle opening being orientedhorizontally).

Pressurized matrix may be directed into body 158 at the same time thatthe reinforcement is discharging from nozzle 166 into body 158. Thematrix may infiltrate and at least partially wet (e.g., fully saturateand coat) the reinforcement prior to the reinforcement reaching nozzle168. In some applications, infiltration and/or saturation of thereinforcement with the matrix may be enhanced as a temperature of thematrix is elevated (e.g., as a viscosity of the matrix is decreased). Inthese applications, the temperature may be elevated via one or morecartridges 176 of heater 170. A temperature sensor 178 may beselectively employed by controller 20 to help regulate operation ofcartridges 176 in a feedback-manner. A pressure sensor (not shown)located within body 158 may similarly be employed by controller 20 tohelp regulate a pressure applied to cartridge 110 within module 46.

The reinforcement wetted with matrix (i.e., the composite material) maybe discharged from body 158 through nozzle 168. Like nozzle 166, nozzle168 may also have a cross-sectional (e.g., rectangular) shapesubstantially matching the cross-sectional shape of the reinforcement.An area of the cross-section may taper from a larger upstream end to asmaller downstream end to facilitate threading of the reinforcementthrough nozzle 168. The area of the downstream cross-section may beselected to be larger than a cross-sectional area of the reinforcement,such that a desired amount of matrix clinging to the reinforcement maypass through the downstream cross-section. In one embodiment, thedownstream cross-sectional area of nozzle 168 may be 0-120% greater thanthe cross-sectional area of the reinforcement. A seal 180 may bedisposed annularly between an outer surface of nozzle 168 and an innersurface of body 158, and a fastener (e.g., a nut) 182 may be used topress nozzle 168 into body 158. Body 158 may include one or moreclocking features (e.g., flat lands) that engage one or more clockingfeatures (e.g., flat lands) of nozzle 168, such that body 158, nozzle166, and nozzle 168 (and the reinforcement passing through nozzles 166and 168) may be oriented in a desired manner relative to each other.

Body 158 may be operably mounted to primary plate 26 a (referring toFIGS. 2 and 3) in a thermally isolating manner. For example, a mountingblock 184 may be placed annularly around body 158, with an air gap 186located therebetween. A pair of axially spaced-apart mounting plates 188may extend radially from body 158 outward through air gap 186 andconnected to opposing ends of mounting block 184. Fins, vanes, or otherheat transferring components 190 may extend from mounting block 184 todissipate any excess heat that happens to pass through air gap 186 intothe air before the heat can be transferred into primary plate 26 a.

Modules 50 and 52 may be configured to move together relative to therest of head 16. This movement may occur, for example, before, during,and/or after a severing event (e.g., after completion of a print path,during rethreading and/or during start of a new print path). As shown inFIGS. 19 and 20, modules 50 and 52 may be rigidly connected to eachother via a bracket 192 that translates (e.g., rolls and/or slideslinearly) along a rail 193 (shown only in FIG. 20) affixed to primaryplate 26 a. Bracket 192 may extend through a slot 194 formed withinprimary plate 26 a, with modules 50 and 52 located at a first side ofprimary plate 26 a and rail 193 located at a second side of primaryplate 26 a. An actuator 196 may be mounted to primary plate 26 a at thesecond side, and be mechanically linked to bracket 192. With thisconfiguration, an extension or retraction of actuator 196 may result intranslation of bracket 192 and modules 50, 52 along rail 193. In oneembodiment, actuator 196 is a linear actuator (e.g., a cylinder). It iscontemplated that actuator 196 could alternatively embody a rotaryactuator (e.g., a motor/lead screw), if desired. In either embodiment, asensor may be associated with actuator 196 and configured to generate asignal indicative of a position of actuator 196 and/or modules 50, 52.

It should be noted that, during the translation of bracket 192 andmodules 50, 52 along rail 193, the reinforcement passing through modules50, 52 may remain stationary and slide through modules 50 and 52 ortranslate with modules 50 and 52, depending on an actuation status ofmodule 50. For example, when module 50 is active and clamping thereinforcement at a time of translation, the reinforcement may translatetogether with modules 50 and 52. Otherwise, a tension within thereinforcement may function to hold the reinforcement stationary, movethe reinforcement in a direction opposite the translation, or move thereinforcement in the same direction of the translation at a differentspeed. A rotary sensor 198 may be placed just upstream of module 50 totrack the motion and payout of the reinforcement during these and otherevents. The motion of modules 50, 52 may be coordinated with the motionsof modules 56 and 58 that will be described in more detail below.

As also shown in FIG. 19, modules 56 and 58 may selectively be movedtogether relative to gusset 26 b. For example, a rail 200 may be affixedto gusset 26 b and oriented vertically relative to the perspective ofFIG. 19. In one embodiment, an axis of rail 200 may be generallyparallel (and aligned, in some embodiments) with an axis of coupler 18and/or a final rotation joint of support 14 (referring to FIG. 1). Eachof modules 56 and 58 may include a carriage 202 configured to slideand/or roll along rail 200 in the vertical direction, and a commonlinear actuator 204 may be connected to translate modules 56 and 58together along rail 200. In one embodiment, actuator 204 is directlyconnected to a first end of module 58, and module 56 is connected to amidpoint of module 58. Other configurations are also possible.

The translation direction of modules 50, 52 may be generally alignedwith a center axis of outlet 54 (e.g., of the downstream nozzle168—referring to FIG. 18) and tilted relative to an axis of coupler 18.That is, module 52 may be tilted at an angle ε relative to the axis ofcoupler 18 and relative to extension/retraction motions of module 58 andtranslation of module 56 that will be discussed in more detail below. Inone embodiment, the angle ε may be about 30-60° (e.g., about 45°). Ashallower angle may decrease the formfactor of head 16, while a deeperangle may facilitate greater precision by allowing nozzle 168 to becloser to module 58. The translation of modules 50, 52 may becoordinated with the motions of modules 56 and 58 and described in moredetail below.

In some applications, a counterbalance 205 may be operatively connectedto modules 56 and/or 58. In the embodiment of FIG. 21, counterbalance205 is connected to module 58 via a lever arm 207. A first end of leverarm 207 may be pivotally connected to counterbalance 205, while a secondend may be pivotally connected to module 58. Lever arm 207 may be pinnedto gusset 26 b at a location between the first and second ends. Withthis arrangement, a compacting force imparted by module 58 may remainrelatively constant, regardless of tilting of head 16.

Module 56 may also be configured to selectively move relative to module58. For example, an actuator 206 may link modules 56 and 58 together andbe configured to selectively extend module 56 away from module 58 in theaxial direction of rail 200. Although shown as translating relative tomodule 58, it is contemplated that module 56 could alternatively oradditionally rotate between the stowed and deployed positions, ifdesired.

As shown in FIGS. 22 and 23, module 56 may be an assembly of componentsthat cooperate to sever the reinforcement passing from module 52 tomodule 58. These components may include, among other things, a mountingbracket 208 connecting an output link of actuator 206 to carriage 202(e.g., via a fastener 209), a cutting mechanism (e.g., a rotary blade)210; a cutting actuator (e.g., a rotary motor) 212 connecting mechanism210 to bracket 208 via associated hardware (e.g., bearings, washers,fasteners, shims, etc.) 214, and a cover 216 configured to at leastpartially enclose (e.g., enclose on at least two sides) cuttingmechanism 210. With this configuration, activation of actuator 212 maycause mechanism 210 to rotate such that, during extension of module 56away from module 58, mechanism 210 may sever the reinforcement. Cover216 may protect against unintentional contact with a cutting edge ofmechanism 210. It is contemplated that actuator 212 may be configured toaffect a different motion (e.g., a vibration, a side-to-sidetranslation, etc.) of mechanism 210, if desired. It should be noted thatwhile cutting mechanism 210 has been described as a rotary blade, aserrated, hexagonal, or other polygonal shaped blade may improvesevering, in some situations.

A portion of module 58 is shown enlarged in FIGS. 24, 25 and 26. Asshown in these figures, module 58 may be a self-contained assembly ofmultiple components that interact to selectively compact and at leastpartially cure matrix-wetted reinforcements during discharge from head16. These components may include, among other things, a mounting bracket218 (shown only in FIGS. 24 and 25—omitted from FIG. 26 for clarity)that extends between carriage 202, actuator 204, and module 56; a shaft220 removably connected to bracket 218 (e.g., via one or morefasteners—not shown), a roller subassembly 222 rotationally mounted onshaft 220 via one or more bearings 224, and any number of cure sources226 mounted to one or both of bracket 218 and shaft 220.

Bracket 218 may have an opening formed therein to accommodate andprovide a reaction base for actuator 206 of module 56 (referring to FIG.23) during relative motion induced by actuator 206 between modules 56and 58. An extension of actuator 204 may cause bracket 218 to pressroller subassembly 222 against a material discharging from head 16,thereby compacting the material with a force related to the extensiondistance. In some embodiments, a resilient mechanism (e.g., spring) maybe located between bracket 218 and subassembly 222, such that the forceof the compaction is related to the displacement caused by actuator 206and a spring-force of the resilient mechanism.

In the disclosed embodiment, four different cure sources 226 (e.g.,light sources, such as light pipes that extend from one or more U.V.lights 227 or lasers—shown in FIG. 20) are implemented within module 58.Two of these sources 226 may be mounted directly to shaft 220 at aleading side relative to a movement direction of head 16 (e.g., enteringaxial ends of shaft 220), while two sources 226 may be mounted directlyto bracket 218 at a trailing side. Leading sources 226 may terminatewithin roller subassembly 222, for radiation radially outward through anannular surface of roller subassembly 222 at the tool center point ofhead 16. Trailing sources 226 may terminate just above the materialdischarging from head 16 at a location downstream of roller subassembly222.

The orientation of each source 226 may be designed to provide a desiredlevel of curing to a particular portion of the discharging material. Inone embodiment, a transverse angle β (shown in FIG. 26) located betweena compaction axis 228 of module 58 (e.g., an axis passing in a directionof force exerted by actuator 204 that is substantially normal to asurface of the discharging material being compacted) and an axis of eachsource 226 may be about 20-40° (e.g., about 30°). In this sameembodiment, a fore/aft angle γ (shown in FIG. 24) located betweencompaction axis 228 and the axes of leading sources 226 may be about0-20° (e.g., about 10°), while a fore/aft angle δ (shown in FIG. 24)located between compaction axis 228 and the axes of trailing sources 226may be about 30-60° (e.g., about 45°). As will be explained in moredetail below in reference to FIG. 30, the angle γ may be selected sothat the associated cure energy impinges the material at a trailing sideof a flat patch formed within roller subassembly 222 (e.g., starting ata tool center point in the flat patch and extending rearward). The flatpatch may allow the material to be compressed flat against an adjacentlayer prior to and/or while being cured. The angle δ may be selected toprovide a compact form factor of head 16 at the discharge end, whiledirecting the associated cure energy as close as possible to the toolcenter point of roller subassembly 222. A greater angle δ may allow foreven closer exposure, but the form of head 16 may grow proportionally.The cure energy from leading sources 226 may primarily function to tackthe discharging material in a desired shape and location, while the cureenergy from trailing sources 226 may function to impart a deeper orgreater degree of cure (e.g., a through-cure).

As shown in FIG. 27, roller subassembly 222 may include, among otherthings an internal hub 230 that is rotationally mounted over shaft 220via bearings 224 (referring to FIGS. 24-26), a biasing insert 232mounted over hub 230, a compliant roller 234 mounted over insert 232,and an outer annular cover 236.

Hub 230 may have an inner annular surface 238 that steps radiallyoutward to a larger diameter at opposing axial ends, the larger diameterat each end being configured to internally receive an outer race of acorresponding bearing 224 (referring to FIGS. 25 and 26). The innerraces of bearing 224 may be supported at ends of shaft 220, and anannular gap may exist between inner annular surface 238 of hub 230 andan outer annular surface of shaft 220. In this way, hub 230 may beallowed to rotate freely relative to shaft 220, even during compressingactivities of roller subassembly 222.

Hub 230 may likewise have an outer annular surface 240 that stepsradially inward to a smaller diameter at the opposing axial ends, thesmaller diameter at each end being configured to support correspondingends of roller 234. Roller 234 may include inwardly extending flanges242 (see FIG. 29) that engage the smaller diameters of outer annularsurface 240. This engagement may axially align roller 234 with hub 230.In one embodiment, the compliance of roller 234 may be sufficient torotationally bind roller 234 to hub 230. In other embodiments, anadhesive may be used to rotationally bind roller 234 to hub 230.

A material of hub 230 may be selected to provide rigid internal supportfor the other components of roller subassembly 222, as well as energytransmittance from leading sources 226 radially outward to the toolcenter point of head 16. In the example of FIG. 27, hub 230 isfabricated from a clear acrylic material (e.g., an acrylic core coatedwith an FEP sleeve). It has been found, however, that in someapplications, the acrylic material may scatter or diffuse the cureenergy undesirably. In these applications, an alternative material maybe used. For example, as illustrated in FIG. 28, hub 230 may befabricated from an opaque material (e.g., Delrin). Since the opaquematerial may not transmit the cure energy sufficiently, any number ofaxially extending circumferential slots 246 may be distributed aroundhub 230 and pass from inner surface 238 through outer surface 240. Slots246 may facilitate the transmission of cure energy from leading sources226 radially outward.

An annular gap may be present between outer annular surface 240 of hub230 and an inner annular surface 244 of roller 234 (e.g., locatedaxially between flanges 242). Insert 232 may be radially compressed,placed into this gap, and released such that a radial expansion ofinsert 232 biases insert 232 against inner surface 244 of roller 234.This bias may help urge any compressed portions of roller 234 to adesired cylindrical shape.

A material of insert 232 may be selected to provide the internal biasingsupport for roller 234. In the example of FIG. 27, insert 232 isfabricated from a spring steel. Since spring steel may not transmit cureenergy sufficiently, slots 248 similar to slots 246 may be distributedaround and pass radially through insert 232.

As will be explained in more detail below, any number of indexingfeatures 250 may be formed within insert 232 to help align slots 248with other features of roller assembly 222. In the disclosed example,features 250 may include one or more tabs that extend axially from aperiphery of insert 232 at one or more axial ends. It is contemplated,however, that other indexing features known in the art (e.g., detents,catches, dogs, pawls, etc.) could be implemented, if desired.

An exemplary roller 234 is illustrated in detail in FIG. 29. As shown inthis figure, flanges 242 may be configured to selectively compress in aradial direction (e.g., in a direction along compression axis228—referring to FIG. 26) at the tool center point of head 16 duringcompaction of the material discharging from head 16. For example, eachflange 242 may include an inner race 252 that is separated from an outersurface of roller 234 by an annular gap 254. Any number of flexures 256may extend from a tangent at inner race 252 radially through gap 254 tothe annular surface of roller 234. Flexures 256 may function to bias theannular surface of roller 234 radially outward toward a nominal annularposition about a center axis of roller assembly 222. During compactionat the tool center point against the discharging material, the portionof the annular surface engaging the material may be pressed radiallyinward. This pressing may cause flexures 256 to collapse until gap 254is reduced or eliminated at the tool center point.

As shown in FIG. 30, the collapse of flexures 256 may result in the flatpatch 258 discussed above. Patch 258 may help to press the dischargingmaterial flat against an underlying surface, while also facilitatingseparation of the material at a trailing side (e.g., relative to anormal travel direction of head 16 represented by an arrow 259). In oneembodiment, gap 254 and the associated collapse dimension of roller 234may be about equal to 4-5% of an outer diameter of roller 234. Thiscollapse dimension may result in the flat patch 258 having a length inthe travel direction of about 40-45% of the outer diameter. As discussedabove, the angle γ of the leading sources 226 may be about 0-20°, suchthat the discharging material may be compacted within a leading half ofpatch 258 and exposed to cure energy only in the trailing half.

A material of roller 234 may be selected to provide for theabove-discussed flexing and to withstand the curing environment (e.g.,electromagnetic radiation generated by sources 226 and any resultingexothermic reactions), without permanently deforming. In one example,roller 234 is fabricated from silicone having a hardness of about 20-50A-Shore (e.g., about 40 A-Shore). To prevent undesired scattering ordiffusion of cure energy, the silicone may be dyed or coated with anenergy blocking tint. To facilitate energy transmission through patch258, slots 260 similar to slots 246 and 248 may be formed within theouter annular surface of roller 234.

In an alternative embodiment shown in FIG. 31, the silicone of roller234 may be left clear or at least partially transparent. In thisembodiment, slots 260 may be omitted.

In one embodiment, indexing features 250 of insert 232 discussed abovemay interlock with flexures 256, such that slots 246, 248 and 260 alignwith each other. For example, an indexing feature 250 may pass betweeneach pairing of adjacent flexures 256 (e.g., within gap 254).

To prevent the materials being compacted from sticking to roller 234and/or being disrupted by slots 260, roller 234 may be wrapped withcover 236. Cover 236 may be at least partially transparent (e.g., about70-99% transparent) to the energy (e.g., to light energy having a350-450 nm wavelength, such as a wavelength of about 405 nm). Cover 236may be fabricated from a low-friction material (e.g.,Polytetrafluoroethylene—PTFE, Fluorinated ethylene propylene—FEP, etc.).In one example, FEP may be utilized for cover 236 due to its greatertransparency when compared with PTFE.

Because cure energy may be directed through roller subassembly 222 tothe matrix-wetted reinforcement, curing at (e.g., just before, directlyover, and/or just after) the TCP may be possible. It is contemplatedthat enough curing may take place to tack the reinforcement beforelittle, if any, movement of the reinforcement away from the TCP locationhas occurred. This may improve placement accuracy of the reinforcement.It is also contemplated that the matrix may be cured only at an outersurface (e.g., enough to tack and/or maintain a desired shape) or thatthe matrix may be through-cured via exposure to only the energy fromsources 226 (in addition to or without any extraneous environmentalexposure). In some applications, however, additional energy exposure(e.g., oven baking, autoclave heating, etc.) after completion ofstructure 12 may be required.

FIG. 32 illustrates an alternative embodiment of roller 234. As shown inthis embodiment, slots 260 may be spaced further apart and orientedobliquely relative to axial and radial directions of roller 234. It hasbeen found that, in some applications, greater interlaminar shearstrength may be achieved when adjacent tracks of material are dischargedand compressed together while still at least partially wet. For example,when matrix at sides of the adjacent tracks are left at least partially(e.g., substantially) uncured before compression and thereafter curedtogether at the same time, a greater interlaminar shear strength may beachieved. In these applications, the exemplary roller 234 of FIG. 32 mayallow enough cure energy from sources 262 to reach the compactingmaterial to hold the material in place, while still leaving some (e.g.,most) of the material uncured. FIG. 33 illustrates material that hasbeen compacted by roller 234, the material having sections 264 that areat least partially cured (e.g., by leading sources 262) and sections 266that are cured to a lesser degree or that are completely uncured.

As can be seen in FIG. 32, sections 264 may make up a minor portion(e.g., less than 10%) of the discharged material. In addition,transverse edges of the material may only be cured at points 268 thatare spaced apart from each other in the length or axial direction of thedischarged reinforcements. An angle θ of slots 260 and the correspondingsections 264 relative to the length or axial direction of the dischargedreinforcements may be selected to provide a desired spacing betweenpoints 268 and/or a desired ratio of sections 264 to sections 266. Inthe disclosed embodiment, the angle θ may be about 30-60° (e.g., about45°).

As shown in FIGS. 34, 35, 36, 37 and 38, modules 52, 56 and 58 may beselectively moved (e.g., at a constant rate or a variable rate relatedto material characteristics) to any position between extended andretracted end positions. For example, module 52 (along with module50—referring to FIG. 2) may be moved between a retracted position shownin FIGS. 37 and 38 that is farthest from module 58 and an extendedposition shown in FIG. 36 that is closest to module 58. Likewise, module56 may be moved between a retracted position shown in FIGS. 34-37 thatis farthest from the reinforcement discharging from module 52 and anextended position shown in FIG. 38 that is closest to the reinforcement.Finally, module 58 may be moved between a retracted position shown inFIGS. 34 and 35 and an extended position shown in FIGS. 36-38. Inaddition, module 58 may selectively be biased within a zone (e.g.,within about +/−10 mm) about the extended position during engagementwith the discharging material based on a pressure of module 58 againstthe material. It should be noted that movement (i.e., extension andretraction) of module 58 may result in similar simultaneous motion ofmodule 56, but that module 56 may additionally move (i.e., extend andretract) relative to module 58.

The extensions and retractions of modules 52, 56 and 58 may becoordinated in different ways during various operations of head 16. Forexample, all of modules 52, 56 and 58 may initially be in theirrespective retracted positions (see FIG. 34) at a start of a threadingevent (e.g., just after completion of a severing event). Thereafter,module 52 (i.e., with module 50 clamped against the reinforcement) maybe extended to push reinforcement protruding therefrom to a locationunder module 58 (see FIG. 35). Module 58 may then be extended to contactthe protruding reinforcement (see FIG. 36) and press the reinforcementagainst an underlying layer (not shown). Modules 52, 56 and 58 mayremain in these positions throughout discharging of the reinforcement.

After discharging has terminated, module 52 may be retracted away frommodule 58 to provide clearance for module 56 (see FIG. 37). Module 56may then be extended to sever the reinforcement (see FIG. 38), and thecycle may restart at FIG. 34.

It should be noted that, when modules 52 and 58 are in their extendedpositions, the reinforcement may be directed along the axis of module 52toward module 58 at a nominal tangent to roller 234. This may cause thereinforcement to be directed against roller 234 at times (e.g., whenroller 234 is biased 0 to +10 mm from the neutral position within itsallowed zone).

Distances between the extended positions of modules 52, 56 and 58 mayestablish a minimum length of reinforcement that can be dischargedcompacted and severed. For example, this minimum length may be equal toa distance from mechanism 210 of module 56 to the nip point of module 58along the axis of module 52 (e.g., along the trajectory of thereinforcement). In one embodiment, the minimum length may be about equalto 0.7-0.8 (e.g., about 0.78) times a diameter of roller 234, when anorthogonal offset distance between mechanism 210 and an axis or roller234 is about 0.5-0.6 (e.g., about 0.63) times the diameter or roller234. In other words, the minimum length may be about equal to 1.17-1.6(e.g., about 1.24) times the orthogonal distance. The distance betweenthe extended and retracted positions of module 52 (a.k.a., the feeddistance) may be greater than the minimum length (e.g., about 2× theminimum length). The distance between the extended and retractedpositions of module 56 may be less than the minimum length (e.g., about0.25× the minimum length). In one example, module 52 may actually extendpast module 56 toward module 58—this may reduce the feed distance to beless than the minimum length.

INDUSTRIAL APPLICABILITY

The disclosed system and print head may be used to manufacture compositestructures having any desired cross-sectional size, shape, length,density, and/or strength. The composite structures may include anynumber of different reinforcements of the same or different types,diameters, shapes, configurations, and consists, each coated with acommon matrix. Operation of system 10 will now be described in detailwith reference to FIGS. 1-38.

At a start of a manufacturing event, information regarding a desiredstructure 12 may be loaded into system 10 (e.g., into controller 20 thatis responsible for regulating operations of support 14 and/or head 16).This information may include, among other things, a size (e.g.,diameter, wall thickness, length, etc.), a shape, a contour (e.g., atrajectory), surface features (e.g., ridge size, location, thickness,length; flange size, location, thickness, length; etc.) and finishes,connection geometry (e.g., locations and sizes of couplers, tees,splices, etc.), location-specific matrix stipulations, location-specificreinforcement stipulations, compaction requirements, curingrequirements, etc. It should be noted that this information mayalternatively or additionally be loaded into system 10 at differenttimes and/or continuously during the manufacturing event, if desired.

Based on the component information, one or more different reinforcementsand/or matrixes may be selectively loaded into head 16. For example, oneor more supplies of reinforcement may be loaded onto creel 19 (referringto FIGS. 1-5) of module 44, and one or more cartridges 110 of matrix maybe placed into vessel 112 of module 46.

The reinforcements may then be threaded through head 16 prior to startof the manufacturing event. Threading may include passing thereinforcement from module 44 through guide 80, around redirects 102 ofmodule 48, and then between rollers 146 and 152 of module 50. Thereinforcement may then pass through module 52 and be wetted with matrix.Module 52 may then move to its extended position to place the wettedreinforcement under module 58. Module 58 may then be extended to pressthe wetted reinforcement against an underlying layer. After threading iscomplete, head 16 may be ready to discharge matrix-coatedreinforcements.

At a start of a discharging event, cure sources 226 may be activated,module 50 may be deactivated to release the reinforcement, and head 16may be moved away from a point of anchor to cause the reinforcement tobe pulled out of head 16 and at least partially cured. This dischargemay continue until discharge is complete and/or until head 16 must moveto another location of discharge without discharging material during themove.

As head 16 nears an end of a discharge path, head 16 may be controlledto stop short of a terminal point by a distance equal to the minimumlength discussed above. At this location, motion of head 16 may stop,and sources 226 may be deactivated. Module 52 may be moved to itsretracted position, module 50 may be activated to clamp thereinforcement, and module 56 may be activated and extended to sever thereinforcement. Module 56 may then be deactivated and retracted. Sources226 may be reactivated, and head 16 may be moved to complete thedischarge path. Head 16 may then be moved to a start location of a nextdischarge path, during which time module 58 may be retracted.

In some embodiments, a pressure applied by module 58 on the dischargedmaterial may vary during different events. For example, during asevering event, when module 58 may exert pressure against the materialat a single location for an extended period of time, a pressure ofmodule 58 may be reduced. This may help to avoid denting structure 12 atthe severing location.

During discharge of the wetted reinforcements from head 16, module 58may roll over the reinforcements. A pressure applied by cover 236 maypress the reinforcements against an adjacent (e.g., underlying) layer ofstructure 12, thereby compacting the material. Sources 226 may remainactive during material discharge from head 16 and during compacting,such that at least a portion of the material is cured and hardenedenough to remain tacked to the underlying layer and/or to maintain itsdischarged shape and location. In some embodiments, a majority (e.g.,all) of the matrix may be cured by exposure to energy from source 226.It is contemplated, however, that the sources 226 associated with rollersubassembly 222 may only be active during tacking and anchoring, andthereafter most (e.g., all) of the curing performed only by the trailingsources 226.

It should be noted that the amount of cure energy generated by module 58may be variable. For example, the energy could be generated at levelsthat are related to other parameters (e.g., travel speed) of head 16.For instance, as the travel speed of head 16 increases and the dischargerate of reinforcement from head 16 proportionally increases, the amountof energy generated by module 58 and directed toward the dischargingmaterial may likewise increase. This may allow a consistent unit ofenergy to be received by the matrix coating the reinforcement under arange of conditions. It is also possible that a greater unit of energymay be received during particular conditions (e.g., during anchoring,during free-space printing, at particular geometric locations ofstructure 12, etc.), if desired. Each of sources 226 may beindependently activated, activated in pairs (e.g., leading or trailingsources), or activated simultaneously in a cooperative manner.

The component information may be used to control operation of system 10.For example, the reinforcements may be discharged from head 16 (alongwith the matrix), while support 14 selectively moves head 16 in adesired manner during curing, such that an axis of the resultingstructure 12 follows a desired trajectory (e.g., a free-space,unsupported, 3-D trajectory). In addition, module 46 may be carefullyregulated by controller 20 such that the reinforcement is wetted with aprecise and desired amount of the matrix. For example, based on signalsgenerated by sensor 198 that are indicative of a feed rate of thereinforcement through head 16, controller 20 may selectively increase ordecrease a speed of module 46 to provide a corresponding feed rate ofmatrix to module 52. In this way, regardless of the travel speed of head16, a desired ratio of matrix-to-reinforcement may always be maintained.

As discussed above, during payout of matrix-wetted reinforcement fromhead 16, modules 44 and 48 may together function to maintain a desiredlevel of tension within the reinforcement. It should be noted that thelevel of tension could be variable, in some applications. For example,the tension level could be lower during anchoring and/or shortlythereafter to inhibit pulling of the reinforcement during a time whenadhesion may be lower. The tension level could be reduced in preparationfor severing and/or during a time between material discharge. Higherlevels of tension may be desirable during free-space printing toincrease stability (e.g., to reduce sagging) in the discharged material.Other reasons for varying the tension levels are also contemplated. Thelevel of tension may be adjusted via threshold adjustments associatedwith when actuator 74 is turned on/off and/or what speeds and/or torquesare applied by actuator 74 in response to signals from sensor 104.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the disclosed system andhead. Other embodiments will be apparent to those skilled in the artfrom consideration of the specification and practice of the disclosedsystem and head. For example, while module 48 has been disclosed ascapable of generating signals indicative of tension within thereinforcement that are then used to adjust creel operation (e.g.,payout), it is contemplated that the signals may instead be indicativeof a position of module 48 at a desired constant tension level. In thisexample, creel 19 may be controlled to maintain a buffer about theposition of module 48, such that creel 19 may be kept at a near steadystate regardless of the motion of module 48 and payout of thereinforcement. It is intended that the specification and examples beconsidered as exemplary only, with a true scope being indicated by thefollowing claims and their equivalents.

What is claimed is:
 1. An additive manufacturing system, comprising: asupport; a print head operatively connected to and moveable by thesupport, the print head including: a supply of continuous reinforcement;an outlet configured to discharge the continuous reinforcement; and atensioning module disposed between the supply and outlet, the tensioningmodule being configured to generate a signal indicative of at least oneof a tension in the continuous reinforcement and a position of thetensioner module; and a processor programmed to selectively cause thesupply to dispense the continuous reinforcement based on the signal. 2.The additive manufacturing system of claim 1, further including awetting module configured to wet the continuous reinforcement with amatrix prior to discharge from the outlet, wherein the tensioning moduleis located between the supply and the wetting module.
 3. The additivemanufacturing system of claim 1, wherein the tensioning module includes:a swing arm; at least one redirect located at end of the swing arm andconfigured to receive the continuous reinforcement; a pivot located awayfrom the end of the swing arm; and a rotary sensor configured togenerate the signal during pivoting of the swing arm about the pivot. 4.The additive manufacturing system of claim 3, wherein the at least oneredirect is rotationally mounted to the end of the swing arm.
 5. Theadditive manufacturing system of claim 3, wherein the pivot iscoincident with the at least one redirect.
 6. The additive manufacturingsystem of claim 3, wherein: the at least one redirect is a firstredirect located at a first end of the swing arm; and the tensioningmodule includes a second redirect located at a second end of the swingarm and configured to receive the continuous reinforcement.
 7. Theadditive manufacturing system of claim 6, wherein: the first redirect islocated upstream of the second redirect relative to travel of thecontinuous reinforcement through the print head; and the pivot iscoincident with the first redirect.
 8. The additive manufacturing systemof claim 7, wherein the rotary sensor is associated with the firstredirect.
 9. The additive manufacturing system of claim 7, furtherincluding a counterbalance mounted to the swing arm at the first end.10. The additive manufacturing system of claim 9, further including aspring at the first end and configured to bias the swing arm toward alow-tension position.
 11. The additive manufacturing system of claim 3,further including a counterbalance mounted to the swing arm.
 12. Theadditive manufacturing system of claim 3, further including a hard endstop located at a first side of the swing arm and configured to limit alow-tension position of the swing arm.
 13. The additive manufacturingsystem of claim 12, further including a biased end stop located at asecond side of the swing arm and configured to limit a high-tensionposition of the swing arm.
 14. The additive manufacturing system ofclaim 3, further including a biased end stop located at a first side ofthe swing arm and configured to limit a high-tension position of theswing arm.
 15. The additive manufacturing system of claim 3, furtherincluding a spring configured to bias the swing arm toward a low-tensionposition.
 16. The additive manufacturing system of claim 1, wherein therotary sensor is one of an encoder and a potentiometer.
 17. A method ofadditively manufacturing a composite structure, comprising: directing acontinuous reinforcement from a supply of a print head to an outlet;generating a signal indicative of at least one of a tension in thecontinuous reinforcement and a position of a tensioner module at alocation between the supply and the outlet; and selectively causing thesupply to dispense the continuous reinforcement based on the signal. 18.The method of claim 17, further including: wetting the continuousreinforcement with a matrix at a location inside of the print head; anddischarging the wetted continuous reinforcement through the outlet,wherein generating the signal includes generating the signal indicativeof a tension at the location.
 19. The method of claim 17, furtherincluding pivoting a swing arm with the continuous reinforcement,wherein generating the signal includes generating the signal based onthe pivoting.
 20. The method of claim 19, further includingcounterbalancing the swing arm and biasing the swing arm toward alow-tension position.